The present invention relates to an illumination unit for liquid crystal projection display apparatus and a liquid crystal projection display apparatus. More particularly, it concerns a bright illumination unit for liquid crystal projection display apparatus for efficiently collecting a light emitted from the illumination unit to an illumination surface, or a liquid crystal surface (24), without widening, or rather narrowing, an angle for luminous flux, and concerns a liquid crystal projection display apparatus having it used therein.
Prior illumination units for use in a liquid crystal projection display apparatus are described, for example, in the Japanese Patent Laid-Open Nos. 1-120192 and 3-230404. Most of the prior illumination units, as shown in FIG. 7, are formed of a lamp (1) and a reflector (3). In the figure, reference numerals 11 and 12 indicate light components.
There are prior liquid crystal display apparatuses, for example, a direct sight display apparatus that an image is formed on a light valve as a change of optical characteristic with a given video signal, is illuminated by a light source, and is directly viewed; and a projection display apparatus that an image is projected through a projection lens (25) to a screen (26) as an optical image. Many types of light valves having a liquid crystal display device (23) of transillumination type have been proposed for use in such liquid crystal display apparatuses.
Prior illumination units having the liquid crystal display device (23) of transillumination type for use in the liquid crystal projection display apparatus are described, for example, in the Japanese Patent Laid-Open Nos. 64-38725 and 1-182877. In the prior illumination units, the light emitted from a light source is reflected by one reflector (3) to illuminate the liquid crystal display device (23).
Prior illumination units, like the present invention, formed of a plurality of reflectors (3) or a plurality of reflectors (3) and a condenser lens (14) include disclosures in the Japanese Patent Laid-Open Nos. 58-66909, 2-132403, 3-131835, 4-5643, 4-328538, and 5-11343.
However, the usual illumination units for use in the liquid crystal projection display apparatus cannot have a sufficiently high light utilization coefficient since there are light components, such as the light components (11) in FIG. 7, that are not directed toward the reflector (3), but scatter out.
Also, the usual illumination units have a problem that an actual light emitting gap of a metal halide lamp used as a light source in the liquid crystal projection display apparatus is too large to have a high light condensing rate.
In order to compensate such a loss, the reflector (3) has to be made larger. However, the large reflector (3) causes the whole apparatus to be made larger and widens an angle for luminous flux which is an angle of the light coming onto the liquid crystal display device (23), which is an illumination surface. With increase of the angle for luminous flux, the following problems are caused, resulting in difficulty of increasing the brightness of the liquid crystal display apparatus.
First, operation of a microlens array (42) is described below. The liquid crystal display device (23), as shown in FIG. 11, has many picture element electrodes (39) acting as light valves arranged in a matrix fashion. There is a light shutting portion (40) around each of the picture element electrodes (39). The light coming to the light shutting portion (40) cannot be effectively used as being interrupted by it. The term "angular aperture" as used herein denotes a ratio of area of the picture element electrode (39) allowing the light to pass to an area (45) corresponding to one picture element. If the angular aperture is increased, the liquid crystal display apparatus can be made brighter. However, this depends on the liquid crystal display device (23). For this reason, the reflector (3) is made to have the microlenses 42 on the incoming light side of the picture element electrodes (39) in the matrix fashion corresponding to the respective picture element electrodes (39). The microlenses 42 can collect the light to enter the picture element electrodes (39) to increase the effective angular aperture. However, as shown in FIG. 20, when the angle of light irradiated to the microlens increases, the effect of improvement of the effective numerical aperture by the microlens reduces. When the angle increases further, the effective numerical aperture becomes lower than that when no microlens is provided and the brightness of the projected images reduces inversely. The effective angular aperture cannot be increased. This causes the brightness of the projected image to be lowered. This is not desirable. FIG. 20 depicts a graph illustrating the effective angular aperture of the liquid crystal display device (23) by the microlens array (42) to the angle for luminous flux from the light source 1 to the liquid crystal display device (23) in the liquid crystal projection display apparatus having the microlens array (42) used therein. In FIG. 20, letter A denotes the effective angular aperture without microlens array (42), and letter B is the effective angular aperture with the microlens array (42). We can see in FIG. 20 that the effective angular aperture is decreased with the angle for luminous flux. We can also see that the effective angular aperture (%) is decreased at a larger angle for luminous flux as compared with that of no microlens array (42).
Thus, as described above, even if the reflector (3) is made larger to increase the light collection rate, the angle for luminous flux is made larger at the same time. This decreases the effective angular aperture of the microlens array (42). A total light utilization coefficient cannot be increased.